Phylum Nemertea is found to have uncommon or parasitic habits and have been found to exhibit physiological, behavioral and morphological adaptations correlating with their host’s way of life (Fleming ; Gibson, 1981). The genus Carcinonemertes has been found to exhibit definite relationships with its crab hosts. The first actual observations of a direct nutritional and physiological dependence of the nemertean on the host was made by Wickham (1979a). He found Carcinonemertes errans feeding on the eggs of the Dungeness crab.

Only on female crabs brooding eggs, juvenile worms reach maturity and reproduce. The degree of infestation is extremely variable and can be very high. Humes (1942) recorded at least 1000 worms in the gill chambers of one crab and Pearse (1949) found an average of 83 worms per host. According to Gibson (1972), immature worms are generally found between the gill lamellae. Immature worms in the branchial chamber are enclosed until the host is able to carry the eggs. They then move to the host egg mass to mature. On reaching sexual maturity, Carcinonemertes deposits its eggs amongst the host’s egg mass.

Within the genus Carcinonemertes, 5 species are currently recognized, one of which comprises two varieties. Several host species have been recorded, mostly belonging to the Brachyura (Fleming & Gibson 1981). There has been a single record of a host species within the Leucosiidae (Humes 1942). worms attributed to the genus Carcinonemertes were found to occur on crabs from several localities.


Horsehair worm (left) and the cricket from which it emerged.

Horsehair worms are parasites of certain insects, especially the crickets and grasshoppers. Their common habitat is puddles of water, damp sidewalks, patios, and from bodies of their insect hosts. They can be frightening if one is not used to their look/appearance, these creatures actually not harmful and have no economic importance.

The long, thin structure of these worms is so similar to that of a hair, most scientist thought that they were transformed from the tail hair of horses. Horse hairs frequently drop into watering troughs where they can accumulate. Accidentally, insects (including those parasitized by horsehair worms) also frequently fall into the water of horse troughs and die. Horsehair worms which emerge from parasitized insects were seen swimming in water troughs and supposed to have spontaneously transformed from the long horse hairs, this is how the name horse hair worm was derived (Everett 1996).

(K├Âlliker, 1845): Carcinonemertes carcinophila Description:Sexually mature individuals, which live on the egg masses of crabs, are 20-70 mm long. Juvenile worms, found on the host gills, reach about 15 mm in length. The body is slender and yellowish, orange, pale reddish, rose pink or bright brick red in color. Two small eyes near the anterior tip, occasionally these may have become fragmented (C. carcinophila-head).The anal blood vessel commissure passes ventrally below the posterior end of the intestine. Ovaries are arranged in a single row on each side of the intestine.Habitat:The entire life cycle is spent on the crab hosts, although artificially removed specimens are capable of surviving for several weeks in clean sea water. In the British Isles recorded hosts are Carcinus maenas and Liocarcinus depurator . 40-50 or more nemerteans may be found upon a single host. Juvenile worms live among their host gill filaments, adhering to them by means of sticky mucous secretions. When the host is heavily infected, some of the gill plates may become damaged, blackened and degenerated. The nemerteans remain on the gills until the host produces eggs, then migrating to the egg masses where they reach sexual maturity and lay their own eggs in mucous tubes. The newly hatched nemerteans tend to remain among the host eggs until the end of the breeding period, after which they move to the gill chamber.Distribution:Found on galatheid, portunid and xanthid crabs from Europe to the Atlantic coast of North America. The related variety, Carcinonemertes carcinophila imminuta, which differs from the European form in length and in the size of the proboscis armature, is found in the Gulf of Mexico, the West Indies, Central America and Brazil
worm egg string
worm egg string

Eye spots
Since horsehair worms are parasitic, they are assumed to be beneficial in the control of certain insects. Its true value as a parasite, however, is questionable because the worm does not kill its host until it matures. Horsehair worms do not parasitize humans or pets, they are parasites of insects. Therefore, these creatures are primarily of interest as one of nature’s oddities (biological controls). If their presence in a swimming pool is bothersome, they can be safely removed by hand or with a net.

Records of human accidental parasitism with Parachordodes, Paragordius, or Gordius are uncommon in the literature, although many have been identified in different parts of the world from specimens recovered from the mouth, urethra, and anus. Six human cases of Gordius sp. have been reported in Japan. In these cases, worms were vomited and excreted in the feces and from anus. A human case of a Gordius worm found in the vomitus and another case of a Parachordodes worm found in the urinary system have also been reported in Korea (Kagei N ; Oshima, 1996).
During the major phase of their life cycle, horsehair worm is parasitic. After development in the host, they emerge to copulate in freshwater or in the marine environment. The emergence of the larvae from eggs also takes place in the free-living phase but then as a larva, which are equipped with hooks and stylets infect their hosts. The life cycle, especially in the parasitic phase, is still a black box for the majority of species. Gordiid larvae can be found encysted in many aquatic animals, ranging from trematodes parasitic in newts to vertebrates mostly fishes or frogs. However, complete development takes place in a far more limited host spectrum.

As larvae develop fully or nearly so (several weeks or months), they break through the body wall of the host (in moist habitats) and become free-living. Other people believe that young worm larvae bore into or are swallowed by immature stages of water-containing insects such as mayflies, dragon flies, or beetles. When the host emerges from the water as free-flying adult, the mature horsehair worm breaks out of the body cavity. Grasshoppers, crickets, etc. may be a second host if they eat the dead, infested mayfly adults. It appears that the host must first come in contact with water to enable horsehair worms to escape the body cavity
After the water level drops, the exposed vegetation is eaten by a grasshopper or cricket. The cyst covering dissolves, permitting juvenile worms to bore through the gut wall and into the body cavity of the host. All nutrients are absorbed across the body wall of the worm, as no digestive like alimentary system is present (Rhaesa ; Schmidtrhaesa, 1997).

1. Fleming LC, ; Gibson R. 1981. A new genus and species of monostiliferous hoplonemerteans, ectohabitant on lobsters. J. exp. mar. Biol. Ecol. 52: 79-93.

2. Gibson R. 1972. Nemerteans. Hutchinson University Library, London.

3. Humes AG. 1942. The morphology, taxonomy and bionomics of the nemertean genus Carcinonemertes. Ill. Biol. Monogr. 18: 1-105.

4. Kagei N, Oshima T, Inoue I, Kumasaki T. 1996. First human case on gordid worm in Japan (Nematomorpha: Gordiidae) Jpn J Parasitol: 79-81.

5. Kolliker AV. 1845. Ueber drei neue Gattungen von Wurmen Lineola, Chloraima, Polycystia, neue Wurmgattungen und neue Arten von Nemertes. – Verh. schweiz. naturf. Ges. Chur. 29: 86-98.

6. Pearse AS. 1949. Observations on flatworms and Nemerteans collected at Beaufort, N.C. Proceedings of the United States National Museum. 100: 25-38.
7. Wickham DE. 1979a. Predation by the Nemertean Carcinonemertes errans on eggs of the Dungeness crab, Cancer magister. Marine Biology. 55: 45-53.